Tuberculosis (TB) is a major and still neglected cause of death and disability with around 2 million deaths worldwide in 2009 and 9 million infections. There is more tuberculosis today than at any other time in history. The emergence of drug resistant strains and confluence with HIV epidemic has turned TB into a global public health crisis. Although, available drug regimens can cure most patients, emergence of MDR, SDR and XDR-TB coupled with insufficient global drug pipeline, justifies continued efforts towards development of new drugs with new mode of action and novel structures. It has therefore now become imperative to identify new lead molecules for the development of new tuberculostatic drugs.
Family Lamiaceae and diterpenes class of compounds, particularly from Leucas genus has been the subject matter of interest for the study of anti-tubercular drugs. Reference may be made to International Journal of Pharm Tech Research, ISSN: 0974-4304 Vol. 3, No. 2, pp 872-880, published in. April-June 2011 titled “A Review on Anti-Tubercular Plants” by Vikrant Arya et.al discloses various plant drugs along with their chemical constituents like alkaloids, flavonoids, tannins, xanthones, triterpenes, quinones etc. responsible for anti-tubercular activity. Table 2 in the said article gives a brief description of common anti-tubercular plants from Ayurveda. Table 3 lists anti-tubercular plants of foreign origin wherein, diterpenes are isolated from plant (i) Salvia hypargeia of family Lamiaceae and (ii) Salvia sclarea of Family Lamiaceae using alcohol as a solvent.
Article titled ‘Antimycobacterial natural products’ by Brent R. Copp in Nat. Prod. Rep., 2003, 20, 535-557, having DOI: 10.1039/b212154a discloses natural products having anti-TB activity. The article further discloses Terpenes with anti-TB activity. (i) Halogenated monoterpenes originally isolated from the marine red alga Plocamium cartilagineum, exhibits potent anti-algal activity as well as antimycobacterial activity towards M. tuberculosis H37Rv with an MIC of 32 μg/ml and M. avium (MIC 64 μg/ml). (ii) Also identified as exhibiting antitubercular (M. tuberculosis H37Rv) activity in this study were juniperexcelsic acid (MIC 14.4 μg/ml) (205) and sclareol (MIC6.0 μg/ml) (206).

Article titled “Phytochemical Investigation and Antimicrobial Activity of Leucas cephalotes (Roth.) Spreng. Whole Herb by Katara Antariksh et.al in Der Pharmacia Lettre, 2010, 2(4):284-296; discloses Leucas cephalotes Roth. Spreng (Lamiaceae) to cure various disorders. The plant has antipyretic action and also considered to be stimulant, expectorant, aperient, diaphoretic, insecticidal and emmenagogue. Leucas cephalotes (Roth.) Spreng. whole herb contains new labdane, norlabdane and abietane type diterpenes and protostane type triterpenes, together with common triterpene, five sterols and eight flavones.
Different extracts of the transverse section of stem, leaf and root were subjected to various phytochemical tests, to identify the active constituents, shown in Table 2 in the said article. Ethanolic and methanolic extracts were found to have more active constituents compared to other extracts. Phytochemicals such as carbohydrate, proteins and amino acids, glycosides, flavonoids, tannins and phenols and steroids were commonly found in most of the extracts. (However, the extracts do not mention diterpenes as a phytoconstituent).
Article titled “Diterpenes from Leucas aspera Inhibiting Prostaglandin-Induced Contractions” by Samir Kumar Sadhu et.al in J. Nat. Prod., 2006, 69 (7), pp 988-994 and having DOI: 10.1021/np058118m relates to four new diterpenes, leucasperones A (1) and B (2) and leucasperols A (3) and B (4), and three new isopimarane glycosides, leucasperosides A, B, and C (5-7), together with the known compounds asperphenamate, maslinic acid, (−)-isololiolide, and linifolioside. leucasperone A (1), leucasperosides A (5) and B (6), and linifolioside showed inhibition of prostaglandin-induced contractions.

In the search for such new molecules, a wide range of plant extracts were screened for their inhibitory potential against the tuberculosis. The extracts of Leucas stelligera unexpectedly showed most potent anti-tubercular property among the extracts tested. Leucas stelligera is an edible plant with leaves eaten as vegetable. No chemical and pharmacological work is reported on this species.